In recent years, a head-mounted display and a glass-type wearable device, both of which are equipped with a device for detecting eye motions, have been publicly known. Taking an instance of these devices, it is known that Google Glass (registered trademark), of which an infrared sensor is capable of detecting the upward motion and blink/wink of the eye, as well as attachment/detachment of a device, allows the user, depending on the settings, to take pictures or attach/detach a device by blinking and to switch a display on by moving the eyes upward
In addition to devices for detecting eye motions such as blinking or winking to take an action, a method for detecting the position of the iris on the image of the area of the eye captured by a camera is known. Taking an instance, in order to detect the position of the iris of the eye, some devices use any of existing techniques such as template matching to match the iris on the eye image with the template image in terms of the iris pattern (grayscale pattern of the iris).
Moreover, the directions and speeds of eye motions may be detected by detecting the aforementioned position of the iris individually on the consecutive eye images and, for instance, projecting the individual positions in a 2-dimensional or 3-dimensional coordinate system to compare or find differences between consecutive coordinate values in the coordinate system. Furthermore, the aforementioned method, which allows the user to trace the direction of an eye motion or detects the patterns of the directions and speeds of eye motions and compares with known normal patterns to find a difference, if any, may have applications such as identification of any abnormality, bad condition or disease in the body. Taking an example, in normal cases, eye rotational motions (eye motions) occur along the visual line direction as a rotation axis when the tilted head returns to its original position. If the eye motions occur with the head not tilted, car sickness or motion sickness may be suspected (for instance, NPL 1).
Moreover, in some cases, when the image of an eye, of which surface is carved, is captured, the distance of a light path between the center of a target eye and a camera lens may vary, making it difficult to bring the camera into focus thereon and causing failure to focus when the eye moves. To solve this problem, one idea makes an attempt to use a camera with a large depth of focus in order to bring a whole area including the center of the eye and an area around the eye into focus. However, to this end, intense lighting is needed, which may affects the eyes. To address this problem, another idea has been designed so that the center of the pupil is detected and the focusing is controlled in connection with the center of the pupil to allow the focus to be correctly brought into the eye, even if it moves (for instance, PL 1).
Furthermore, one other method uses a cornea reflected image (Purkinjje's image), which take advantage of a difference in the center of rotation between the eye and cornea, to measure eye motions and the vertical and horizontal components of a visual line at a high accuracy.
In addition, the inventors of the present invention have proposed a method to measure eye rotations by identifying a blood vessel of a predetermined pattern in the vicinity of an iris in a white area (the portion, in which a sclerotic coat and a conjunctiva are exposed) of the eye in the reference state and detecting an outer peripheral edge of the iris based on the position of the end point of the identified blood vessel to solve the problem (described later) with aforementioned iris pattern detection (for instance, PL 2).